Correlation of transcranial doppler (TCD) parameters with jugular bulb venous oxygen saturation (SjO₂)

Introduction

Disturbances of the cerebral circulation play a key role in the pathophysiology of head injury. TCD ultrasonography, a non invasive bedside technique, and SjO₂ monitoring, an invasive technique which has some risk factors, are methods of assessing cerebral hemodynamics. The purpose of the study was to examine the relationships between TCD parameters and SjO₂ measurements in patients with head injury.

Methods and materials

Forty patients (35 ± 18 years) with severe head injury (Glasgow coma scale < 8) were included in the study. All patients were mechanically ventilated, sedated and paralyzed. Continuous monitoring of intracranial pressure (ICP), arterial pressure, pulse oximetry and SjO₂ were performed in every patient. Multiple TCD examinations (total 150) were performed during the first five ICU days. The TCD parameters were: maximum velocity (V_max), minimum velocity (V_min), and pulsatility index (PI). The findings from TCD were compared with SjO₂ values using the method of Pearson's product moment coefficient of correlation and linear regression analysis.

Results

Among TCD parameters PI was found to be correlated with SjO₂. There was a leak correlation between PI and SjO₂, for SjO₂ values below 75% (r = -0.51, P < 0.01). A breakpoint SjO₂ value of 75% was demonstrated above which there was no correlation between PI and SjO₂ (r = -0.59, P > 0.05). With the same method V_max and V_min were unable to provide more information.

Conclusion

The pulsatility index (PI) cannot predict changes of SjO₂ values. Therefore a combination of TCD and SjO₂ monitoring can provide better access to cerebral hemodynamics.